The desirability of varying valve lift, as desired, in a vehicle engine so as to improve engine operation and fuel economy at all engine speeds has long been recognized. Accordingly, various types of variable valve lift train mechanisms have been proposed.
One such type of variable valve timing and lifting system for overhead cam engines with 2, 3 or 4 valves per cylinder, which has been proposed and built by Fiat Auto S.p.A. of Torino, Italy, uses the longitudinal movement of an overhead camshaft to provide different valve lifting due to conical cam with each such conical cam engaging a multiple piece direct acting valve lifter which includes a cam follower or foot operatively and pivotally supported by a pivotal shaft element for actuating a conventional cylindrical tappet, the latter being slidably journaled in a tappet guide bore provided for this purpose in the cylinder head of an engine, to control the opening and closing movement of an associated valve, either intake or exhaust, and a guide to, in effect, maintain the orientation of the cam follower or foot so that it can pivot about a pivot axis located at right angles to the rotating axis of the overhead camshaft.
In such prior known multiple piece direct acting valve lifters as described hereinabove, even though the cam follower or foot of the lifter is pivotably supported so that it will ride substantially flat against the surface of an associated cam, the pivotal movement of the cam follower or foot on its pivotal shaft support element is not a true rolling contact movement but instead it is actually a sliding motion, which results in a relatively high frictional loss in such a lifter.
Another example of a valve lifter for following a conical cam is shown in U.S. Pat. No. 3,303,833 to Melling wherein the follower has a ball and socket coupling to the lifter body. The pivoting action is a sliding motion between the ball surface and the socket surface.
To avoid the frictional loss in such lifters it is here proposed to incorporate a rolling contact, particularly a cardanic rolling motion, into a valve lifter to allow pivoting of a follower without sliding motion. The U.S. Pat. No. 4,393,820 to Maki et al entitled "Rolling Contact Arm and Pivot", which is incorporated herein by reference, discloses the details of cardanic rolling motion as applied to a valve train, particularly to a rocker arm pivot. The geometrical relationships and the freedom from sliding are fully explained therein. To further avoid frictional loss it is also proposed here to provide a rotating cam follower to overcome the wear due to sliding cam action on the lifter.